Amplifier for a video signal from an image pick-up device

Abstract

A clamping circuit in a video chain of a camera features a series L-C network in a feedback circuit. Interference in the video signal, resulting from the occurrence of microphony in the pick-up tube, can thus be suppressed. When the L-C network is suitably detuned, the resonant frequency signal (microphony frequency) of the grid of the pick-up tube can be fully compensated for in the video signal as regards amplitude and phase using adequate feedback.

What is claimed is: 
     
       1. A video amplifier for a video signal generated in an image pick-up device, said video amplifier comprising an amplifier stage having an input adapted to receive a video signal and an output, a sampling circuit means having an input coupled to said amplifier output and an output for sampling an output signal from the amplifier stage during the line flyback period, a comparison circuit having a pair of inputs, one input coupled to said sampling means output and the second input adapted to receive a reference signal from a reference source respectively and an output means for providing a correction signal which is proportional to the difference between the reference signal and the output signal from the amplifier stage, and means for compensating for microphonic signals generated in said pick-up device comprising a resonance network coupled between the output of the comparison circuit and the amplifier stage. 
     
     
       2. A video amplifier as claimed in claim 1, wherein said resonant network is a series L.C. network. 
     
     
       3. A video amplifier as claimed in claim 1, wherein the comparison circuit comprises a differential amplifier having a non inverting input coupled to the output of said sampling circuit and an inverting input coupled to said reference source, and a feedback element coupled between the output of said differential amplifier and its inverting input. 
     
     
       4. A video amplifier as claimed in claim 3, wherein said feedback element comprises a capacitor, said differential amplifier operating as an integrator. 
     
     
       5. A video amplifier as claimed in claim 3, wherein said resonant network comprises a series LC network.